A disk drive system is a digital data storage device that stores information within tracks on a storage disk. The storage disk may, for example, include a magnetic, an optical, or a magneto-optical material that is capable of storing data. During operation of the disk drive, the disk is rotated about a central axis. To read data from or write data to the disk, a magnetic transducer is positioned above a desired track of the disk while the disk is spinning.
A conventional magnetic disk drive, generally designated 10, is illustrated in FIG. 1. The disk drive includes a storage disk 12 that is rotated by a spin motor 14. The spin motor 14 is mounted to a base plate 16. An actuator arm assembly 18 is also mounted to the base plate 16.
The actuator arm assembly 18 includes a transducer 20 (i.e., head) mounted to an actuator arm 22 that can rotate about a bearing assembly 26. The actuator arm assembly 18 includes a voice coil motor (VCM) 28, which moves the transducer 20 relative to the disk 12. The spin motor 14, VCM 28 and transducer 20 are coupled to a number of electronic circuits 30 mounted to a printed circuit board 32. The electronic circuits 30 typically include one or more read channel chips, a microprocessor-based controller and a random access memory (RAM), among other components.
Instead of having a single disk 12 as shown in FIG. 1, as is well-known in the art, the disk drive 10 may include a plurality of disks 12. In such case, each of the plurality of disks 12 may have two sides, with magnetic storage, optical storage, and/or magneto-optical storage material on each of those sides. Therefore, the disk drive 10 can include a plurality of actuator arm assemblies 18, each of the assemblies 18 being adjacent to a different recordable side of the plurality of disks, and configured to read and/or write data thereon.
Referring now to FIG. 2, data is stored on the disk 12 within a number of concentric tracks 40 (or cylinders). Each track is divided into a plurality of sectors 42. Each sector 42 is further divided into a servo region 44 and a data region 46.
The servo regions 44 of the disk 12 are used to, among other functions, accurately position the transducer 20 so that data can be properly written onto and/or read from the disk 12. The data regions 46 are where non-servo related data (i.e., user data) is stored and/or retrieved. Such data, upon proper conditions, may be overwritten.
FIG. 3 shows portions of tracks 40 for the disk 12 drawn in a straight, rather than arcuate, fashion for ease of depiction. An X-axis indicates a tangential direction along the tracks, and a Y-axis indicates a radial direction relative to the tracks. To accurately write data to and/or read data from the data region 46 of the disk 12 (see FIG. 2), it is desirable to maintain the transducer 20 in a relatively fixed position with respect to a given track's centerline 48 during each of the writing and reading procedures. Tracks n−2 through n+1, including their corresponding centerlines 48, are shown in FIG. 3.
To assist in controlling the position of the transducer 20 relative to the track centerline 48, the servo region 44 includes, among other information, servo information in the form of servo patterns 50 that can include one or more groups of servo bursts, as is well-known in the art. First, second, third and fourth servo bursts 52, 54, 56, 58 (commonly referred to as A, B, C and D servo bursts, respectively) are shown in FIG. 3. The servo bursts 52, 54, 56, 58 are accurately positioned relative to the centerline 48 of each track 40. Unlike information in the data region 46, servo bursts 52, 54, 56, 58 may not be overwritten or erased during normal operation of the disk drive 10.
As the transducer 20 is positioned over a track 40 (i.e., during a track following procedure), it reads the servo information included in the servo regions 44 of the track 40, one servo region 44 at a time. The servo information is used to, among other things, generate a position error signal (PES) as a function of a misalignment between the transducer 12 and a desired position relative to the track centerline 48. As is well-known in the art, the PES signals are input to a servo control loop (not shown) which performs calculations and outputs a servo compensation signal which controls the VCM 28 to, ideally, place the transducer 12 at the desired position relative to the track centerline 48.
Although the servo region 44 and data region 46 are shown in FIG. 3 as having a common track centerline 48, they may have different track centerlines, such that the transducer 20 is moved a predetermined distance from one of the track centerlines of the servo region 44 to be positioned over one of the track centerlines of the data region 46.
A servo track writer (STW) can be used to write servo regions 44, including their corresponding fields, onto the surface(s) of the disk 12 during the manufacturing process. The STW controls the transducers 20 corresponding to each disk surface of the disk drive system 10 to write the servo regions 44. In order to precisely write the servo regions 44 at desired locations on the disk 12, the STW directs each transducer 20 to write in small steps, with each step having a width (i.e., STW step width 72 as shown in FIG. 3). FIG. 3 illustrates the relationship between the STW step width 72 and the pitch 74 of the servo region 44 for a conventional disk drive system.
As used herein, the term “pitch” is the radial distance between centers of adjacent regions on the surface of a disk 12. For example, a servo track pitch 74 (shown in the data region 46 of FIG. 3) is the distance between the centers of radially adjacent servo regions 44. In contrast, the term “width” is defined as the radial distance from one end to the other end of a single region. For example, a servo track width 75 (shown in the data region 46 of FIG. 3) is the width from one end to another of a single servo region 44.
For each servo region 44, the servo track pitch 74 is generally equivalent to the servo track width 75. However, for data regions 46, the data track pitch 76 is generally different from the actual data track width (not shown) due to, for example, the presence of erase bands which are typically found on both sides of each data region 46. For simplicity, the effects that reduce the data track width are not shown in the figures. Instead, the data track width is shown to be the same as the data track pitch.
The servo track pitch can be based on an expected upper-range of the head geometry for a type of disk drive, and may be stored within a STW for use in writing the servo regions 44 within that type of disk drive. The continuing need for higher capacity disk drives continues to drive a demand for smaller geometry heads. However, present manufacturing techniques may result in an increased geometry variability between manufactured heads as the heads are made smaller. Such head geometry variability can cause a reduction in the manufacturing yield of the heads, and/or may cause a reduction in the operation and/or performance of the disk drives.